The invention relates generally to a transmission protocol for remote control systems, and more particularly, to a transmission protocol for vehicle applications that is energy efficient and has high reliability.
The use of remote control transmitters for activating anti-theft systems and remote entry systems in automotive vehicles is increasing. The remote control transmitters are generally battery operated and emit a coded signal for enabling and disabling particular functions. The transmission must be energy efficient since it is desirable to extend the battery life of the transmitter.
Another desirable attribute in remote control systems is reliable system performance. With increasing implementation of remote control systems, it is increasingly desirable to have the remote control system distinguish between transmissions for its associated transmitter and transmissions from other transmitters. Such a problem occurs when two similar systems transmit simultaneously. When two or more systems transmit simultaneously, the receiver may interpret the transmission as an actual transmission rather than recognizing it as an erroneous transmission.
One transmission protocol for remote generating systems is described in U.S. Pat. No. 5,349,459. The system generates a string of start and stop pairs. The time between each stop and start pulse pair is proportional to a corresponding value in a key code sequence. The system is susceptible to both random and periodic noise. That is, a noise spike or other noise may be determined as valid data. Such a system is also susceptible to jamming by other similarly encoded transmission sources. This system may also interpret two or more simultaneous transmissions as a third data packet and unknowingly try to interpret it as a valid transmission. Another drawback to the system is that each transmitted symbol uses a pair of start and stop bits which is inefficient energy management.
It would therefore be more desirable to provide a remote control protocol capable of determining when a corrupt signal is received while consuming minimal amount of energy for each transmission.